1. Field of the Invention
This invention relates to shaft and boss clamping devices, and in particular to such devices adapted for use in corrosive environments or in food machinery where corrosion is a particular problem.
2. Description of the Prior Art
Shaft and boss clamping devices comprising inner and outer races and a pair of bolted taper rings for wedge-wise forcing the respective races against the shaft and boss are known in the art. Where such devices were formerly used in corrosive environments, the inner and outer races, the pair of taper rings and the clamping bolts have been made of stainless steel to minimize corrosion. Use of stainless steel for these elements, however, has not been completely successful because the stainless steel material, although corrosion resistant, is not sufficiently hard.
In the usual device, each clamping bolt passes through an unthreaded hole in one taper ring and is threadably engaged with the second taper ring. The pair of wedge-shaped taper rings are urged together by rotating the threaded clamping bolts. The clamping surface of the bolts, namely the shoulder surface immediately behind the bolt head, is placed directly against a surface of the unthreaded taper ring, progressively greater force being applied between the clamping surfaces on the bolt and taper ring as the bolts are tightened. Where both the bolts and taper rings are composed of stainless steel, a seizure phenomenon occurs which resists relative movement of the bolt and taper ring clamping surfaces. The seizure prevents the bolts from being further tightened to increase the clamping force. Since the maximum possible clamping force is limited, stainless steel is not used in shaft and boss clamping devices of this type.
Rather than employing stainless steel, the art teaches use of a clamping bolt made of a common steel having an anti-corrosion plating applied thereto. Alternatively, protective grease is applied to the device and the greased area is then covered over. Unfortunately, it is impossible to completely close such a cover. Inevitably, the gas or solution in which the device is used penetrates around the periphery of the cover, or grease escapes to foul the solution. With the lapse of time, the grease deteriorates and/or flows out, so a satisfactory corrosion resistance cannot be indefinitely maintained. Moreover, with food machinery, such grease is unsanitary and even small quantities may affect the taste of the food.
It will therefore be appreciated that the problem of clamping a shaft and boss for food machinery or in a corrosive environment is a difficult one. Use of grease for enhancing corrosion resistance involves substantial drawbacks, and even if an anti-corrosion plating is applied to the bolt, it is impossible to maintain sufficient corrosion resistance over a long period of time. A shaft and boss clamping device that employs the long term corrosion resistance of stainless steel rather than platings or grease has therefore been sorely needed in the art. What has heretofore been lacking in a satisfactory way of avoiding the seizure phenomenon characteristic of stainless steel clamping surfaces.